Thomas Cromwell, 3rd Earl of Ardglass (Strensham, Worcestershire, 29 November 1653 – 11 April 1682) was an English nobleman, the only son of Wingfield Cromwell, 2nd Earl of Ardglass and Mary Russell. He held the subsidiary titles of 3rd Viscount Lecale and 6th Baron Cromwell of Oakham.
He succeeded to the titles of 6th Baron Cromwell of Oakham, in the Peerage of England (1540), 3rd Viscount Lecale, in Ulster, in the Peerage of Ireland (1624) and 3rd Earl of Ardglass, in the Peerage of Ireland (1645) on 3 October 1668. On 29 of the same month and year he matriculated at Christ Church, University of Oxford, Oxford, Oxfordshire.
He married Honora Boyle (d. c. November 1710, bur. 14 November 1710 Saint Patrick's Church, Dublin, County Dublin), sister and in her issue co-heiress of Murrough (Boyle), 1st Viscount Blesington, daughter of The Most Rev. Michael Boyle, DD, Archbishop of Armagh and Lord Chancellor of Ireland, and second wife the Hon. Mary O'Brien, without issue. He was succeeded by his uncle Vere Essex Cromwell, 4th Earl of Ardglass.
His widow married secondly bef. 1687 Francis Cuffe (12 September 1656 - 26 December 1694), Member of Parliament for County Mayo in the Parliament of Ireland, son of Sir James Cuffe of Ballinrobe, County Mayo, and had issue, and married thirdly c. 1700 as his first wife Captain Sir Thomas Burdett, 1st Baronet, of Garahill, County Carlow (14 September 1668 - 14 April 1727), without issue.